Indexable cutting inserts for detachable mounting on a tool holder, are generally made of cemented carbide material or ceramic material and are formed by hot pressing or cold pressing and sintering techniques. These inserts typically are available in standard sizes and frequently employ chip breaker control surfaces in the form of a recess extending around the peripheral edge of the insert to break chips as they are formed during a cutting operation.
Modern N/C machining operations in automated factories put high demand on reliable chip flow, durable tool life, and lower machining costs. General purpose chip breakers and chip breaker provided on negative rake inserts do not produce acceptable chip forms and exhibit chipping in machining ductile materials at high speeds and low ranges of feed and depth of cut.
When machining a ductile material at high speeds, a stationary plastic deformation occurs in the shear zone and the formed chip is continuous and straight with smooth flow on the face of the tool. At low ranges of feed and depth of cut, the continuous straight chip is thin and narrow, therefore, it requires an additional deformation to break. In other words, a higher breaking strain is required. The present invention is directed to an insert which enhances the breakage of thin and narrow chips which are generally created under conditions of low feed and light depths of cut.
U.S. Pat. No. 4,685,844 to McCreery describes an indexable and invertible cutting insert having cutting edges and a positive rake surface which appears convex when viewed in cross section.
U.S. Pat. No. 4,214,845 to Yoshikatsu describes a polygonal throw away insert including an insert body having two opposite, parallel major surfaces and a plurality of sides. A cutting edge is formed along a line where each of the sides joins each of the surfaces. A ramp extends from each cutting edge downwardly towards the center of at least one of the two major surfaces of the insert body. A pair of first chip breaking projections are provided on the ramp adjacent each corner of the insert body in a symmetrical relationship with respective to the bisector of the corner and a second chip breaking projection is provided on the bisector behind the first projections.
U.S. Pat. No. 3,815,192 to Ohtsu describes a polygonal throw away insert to be detachably mounted in a tool holder having a plurality of cutting edges on one major surface of the insert body along the edges of all the sides thereof and a plurality of projection rows provided on said major surface along and spaced from the cutting edges so as to form chip breakers. Adjacent projections in each projection row define chip curling zones therebetween.